Hydraulic cement is any mixture of fine-ground lime, alumina, and silica that will set to a hard product by admixture of water, which combines chemically with the other ingredients to form a hydrate.
Prior to the present invention, there were two principal factory-produced hydraulic cement products used in masonry construction: traditional masonry cement and portland cement/lime mortar mixture. Currently, the U.S. market is divided between these two products. Both types of hydraulic cement products contain portland cement as a major ingredient.
Portland cement is a type of hydraulic cement in the form of a finely divided gray powder composed of limestone, alumina, silica, and iron oxide as tetracalcium aluminoferrate (4CaO.Al.sub.2 O.sub.3.Fe.sub.2 O.sub.3), tricalcium aluminate (3CaO.Al.sub.2 O.sub.3), tricalcium silicate (3CaO.SiO.sub.2), and dicalcium silicate (2CaO.SiO.sub.2). Small amounts of magnesium, sodium, potassium, and sulfur are also present. Hardening does not require air, and will occur under water.
Masonry cement is a class of special cements that typically produce more workable and plastic mortars than portland cement/lime mixtures. Traditional masonry cement is typically not suitable for unreinforced load-bearing masonry construction, specifically in high activity seismic areas because of its reputed low flexural strength, and poor bonding ability. High air content (i.e., 18-20%) and the lack or low level of suitable strength enhancers and bonding agents are usually responsible for the inability to eliminate these deficiencies.
A conventional masonry cement based-masonry mortar is a mixture of a masonry cement, sand, functional additives and water. In general, such masonry mortar does not provide adequate flexural bond strength for use in unreinforced load-bearing masonry construction. To satisfy the need for flexural bond strength, two classes of mortars may be used. One such class of material is a blend of portland cement and lime.
The other recently introduced class of special cement is mortar cement. Mortar cements are proprietary formulations having a variety of compositions, all of them including ground portland cement clinker, ground limestone, and functional additives which may include lime. A mortar cement is required to meet a specification in minimum flexural bond strength, according to ASTM 1329.
Three types of mortar cements, i.e., M, N, and S, are currently specified for use in the masonry construction industry. These types of mortar cements are classified based on their strength properties. Generally, the strength is based on the amount of ground portland clinker, ground limestone, lime, air entraining agent, and other additives. The following Table A describes the physical requirements according to ASTM C-1329 for these mortar cement types.
TABLE A __________________________________________________________________________ Physical Requirements Mortar Cement Type N S M __________________________________________________________________________ Fineness, residue on a 45 .mu.m (No. 325) sieve, max. % 24 24 24 Autoclave expansion, max. % 1.0 1.0 1.0 Time of setting, Gillmore method: Initial set, minutes, not less than 120 90 90 Final set, minutes, not more than 1440 1440 1440 Compressive strength (average of three cubes): The compressive strength of mortar cubes, composed of 1 part cement and 3 parts blended sand (half graded standard sand and half standard 20-30 sand) by volume, prepared and tested accordance with this specification, shall be equal to or higher than the values specified for the ages indicated below: 7 days, MPa (psi) 3.4(500) 9.0(1300) 12.4(1800) 28 days, MPa (psi) 6.2(900) 14.5(2100) 20.0(2900) Flexural bond strength 25 days, min. MPa (psi) 0.5(70) 0.7(100) 0.8(115) Air content of mortar Min. volume % 8 8 8 Max, volume % 16 14 14 Water retention value, min, %, of original flow 70 70 70 __________________________________________________________________________
Portland cement/lime mixtures are used today to produce high flexural bond strength mortars. However, such mortar made with portland cement and lime typically has poor workability. Hence, a need exists for producing a mortar cement that has good flexural bond strength and good workability at a relatively low air content as specified by ASTM C-1329.
Hence, the instant invention relates to a new class of polymer additives for use in mortar cements that meets this need of flexural bond strength and good workability at low air content. This class of polymer additives is characterized by their low adsorption onto portland cement which is a critical component of the mortar cement and is a newly defined class of materials for masonry construction. No prior art has been found that describes the use of the instant polymer additives for this specific application.